This invention relates generally to sound production apparatus and more particularly, but not by way of limitation, to a loudspeaker and tube amplifier system. One particular implementation of this is as a portable guitar amplifier of the type which includes a speaker, an electronic tube amplifier circuit, and a cabinet housing the speaker and circuit.
The cabinets of prior sound production apparatus to which the present invention relates are typically open at the back to allow adequate air flow to keep the tubes from overheating. Such open back, however, allows some of the sound energy from the speaker to be lost out the back. If the back could be closed, much of this energy would be redirected out the front of the apparatus and provide smoother tonality in the low end of the output sound. Thus, there is the need for a sound production apparatus which has an enclosed back but which does not thereby cause overheating damage to the electronics of the apparatus.
A particular implementation of the electronic tube amplifier circuit to which the present invention pertains is specifically a class A electron tube amplifier having two triodes and one pentode. This is typically implemented as a relatively small amplifier with limited player control capability. It would be desirable to provide a simple type of tube amplifier that has enhanced control. Such control should be enabled to allow sufficient amplification without diminishing the musical quality of the signal processed through the amplifier for broadcast through the speaker connected to the circuit.